Monitoring substrate processing using reflected radiation

ABSTRACT

A substrate processing apparatus  27  comprises a chamber  35  capable of processing a substrate  20 , a radiation source  58  to provide a radiation, a radiation polarizer  59  adapted to polarize the radiation to one or more polarization angles that are selected in relation to an orientation  33  of a feature  25  being processed on the substrate  20 , a radiation detector  54  to detect radiation reflected from the substrate  20  during processing and generate a signal, and a controller  100  to process the signal.

BACKGROUND

The invention relates to monitoring the processing of a substrate.

In substrate processing methods, features comprising semiconductor,dielectric, and conductor materials, including but not limited to,silicon, polysilicon, silicon dioxide, aluminum, copper and tungstensilicide materials, are formed on a substrate by, for example, chemicalvapor deposition (CVD), physical vapor deposition (PVD), oxidation,nitridation, ion implantation, and etching processes. In CVD processes,a reactive gas is used to deposit material on the substrate. In PVDprocesses, a target is sputtered to deposit material on the substrate.In oxidation and nitridation processes, an oxide or nitride material,such as silicon dioxide or silicon nitride, is formed on the substrateby exposing the substrate to a suitable gaseous environment. In ionimplantation, ions are implanted into the substrate, In conventionaletching processes, etch-resistant features comprising resist orhard-mask, are formed on the substrate and the exposed portions of thesubstrate between the etch-resistant features (substrate open area) areetched to form patterns of gates, vias, contact holes or interconnectlines.

Conventional methods of monitoring the processing of a substrate or of aprocess conducted in a substrate processing chamber often have problems.The process monitoring methods may be used to stop or change theprocess, for example, after a pre-determined change occurs in a featureor material being processed, after a process stage, or at a processendpoint. For example, in the etching of trenches in a dielectric, suchas silicon dioxide, on a silicon wafer, it may be desirable to stopetching after reaching a predetermined depth. In one conventionalmethod, the time required to etch a particular depth in a substrate iscalculated from a predetermined rate of etching and a starting thicknessof the substrate layer or material being etched. In another method, thepeaks resulting from the constructive and destructive interference ofradiation reflected from the substrate are counted to determine asubstrate etching depth. However, such techniques are often inaccuratewhen the starting thickness of the material on the substrate varies fromone substrate to another or when other process parameters change. It isespecially difficult to accurately monitor an etching process when thesubstrate being etched has a small open area between the etch-resistantfeatures because the process signal from such a region is small relativeto the process signal from other portions of the substrate. It is alsodifficult to determine the depth of a material deposited within a via ortrench on the substrate, for example, during the deposition ofdielectric or metal material into a via or trench, because of the smallarea of the deposited material.

Thus, it is desirable to detect a small change that may occur duringprocessing of a substrate. It is also desirable to quantitativelyevaluate the change, for example, a depth of etching, or a thickness ofthe material deposited upon, the substrate. It is further desirable toaccurately monitor substrate processing during the etching of asubstrate having small open areas or during the deposition of materialinto small areas on the substrate.

SUMMARY

The present invention satisfies these needs. In one aspect, the presentinvention comprises a substrate processing apparatus comprising achamber capable of processing a substrate, a radiation source to providea radiation, a radiation polarizer adapted to polarize the radiation toone or more polarization angles that are selected in relation to anorientation of a feature being processed on the substrate, a radiationdetector to detect radiation reflected from the substrate duringprocessing and generate a signal, and a controller to process thesignal.

In another aspect, the invention comprises a method of processing asubstrate in a process zone, the method comprising the steps ofproviding a substrate in the process zone, setting process conditions toprocess the substrate with an energized gas, providing radiation that ispolarized at one or more polarization angles that are selected inrelation to an orientation of a feature being processed on thesubstrate, detecting radiation reflected from the substrate andgenerating a signal in response to the detected radiation, andprocessing the signal.

In yet another aspect, the invention comprises a substrate processingapparatus comprising a chamber capable of processing a substrate, aradiation source to provide a radiation, a radiation polarizer adaptedto polarize the radiation to a plurality of polarization angles, aradiation detector to detect radiation reflected from the substrateduring processing and generate a signal, and a controller to process thesignal.

In a further aspect, the invention comprises a method of processing asubstrate in a process zone, the method comprising the steps ofproviding a substrate in the process zone, setting process conditions toprocess a feature on the substrate with an energized gas, providingradiation that is polarized to a plurality of polarization angles,detecting radiation reflected from the substrate and generating a signalin response to the detected radiation, and processing the signal.

In another aspect, the invention comprises a substrate processingapparatus comprising a chamber capable of processing a substrate, aradiation source to provide a radiation, a radiation detector to detectradiation reflected from the substrate during processing and generate asignal, and a bandpass filter to filter the signal.

In another aspect, the invention comprises a substrate processing methodcomprising placing a substrate in a process zone, setting processconditions of an energized gas to process the substrate, providing asource of radiation in the process zone, detecting radiation that isreflected from a substrate during processing of the substrate andgenerating a signal, and filtering the signal.

In another aspect, the present invention comprises a substrateprocessing apparatus comprising a process chamber comprising a substratesupport, gas inlet, gas energizer, gas exhaust, and a wall having arecess with a window therein and a mask over the window, and a processmonitoring system capable of monitoring a process that may be conductedin the process chamber, through the window in the recess of the wall.

In a further aspect, the present invention comprises a method ofprocessing a substrate in a chamber, the method comprising, placing thesubstrate in the chamber, providing an energized gas in the chamber toprocess the substrate, masking a window provided in a recess in a wallof the chamber, and monitoring a process that may be conducted in thechamber through the window in the recess in the wall.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will be better understood from the following drawings,description and appended claims, which illustrate examples of theinvention. However, it is to be understood that each of the features canbe used in the invention in general, not merely in the context of aparticular drawing, and the invention includes any combination of thesefeatures.

FIG. 1a is a schematic diagram of a first feature being etched in asubstrate and an apparatus for receiving substrate reflected radiationhaving a plurality of polarization angles;

FIG. 1b is a schematic diagram of another feature being etched in thesubstrate of FIG. 1a, the principal orientation of the second featurebeing different than the principal orientation of the first feature;

FIGS. 2a and 2 b are schematic diagrams showing the constructive anddestructive interference effects occurring when radiation is reflectedfrom features being etched in an oxide layer and from the surface of theetch-resistant material, before and after partially etching thefeatures, respectively;

FIG. 3 is a graph of the relative amplitude of different frequencies ofthe interference signal of the substrate reflected radiation;

FIGS. 4a and 4 b are partial traces of the amplitude of the reflectedradiation detected during the etching of 0.4 micron trenches in asilicon dioxide layer having an open area of 5% and 20%, respectively;

FIGS. 5a and 5 b are graphs of partial traces of the amplitude of thereflected radiation tected during the etching of trenches sized 0.4 and1 micron, respectively, in a silicon dioxide layer ving an open area of30%;

FIG. 6 is a graph showing the quality of the intensity of the summationsignal of reflected radiation as a function of feature size and openarea of exposed silicon dioxide;

FIG. 7 is a graph showing the % frequency response versus normalizedfrequency for multiple passes of the bandpass filter;

FIGS. 8a and 8 b are schematic sectional side views of a chamber andprocess monitoring system according to the present invention;

FIG. 9 is an illustrative block diagram of a computer program suitablefor operating the chamber and monitoring a process performed therein;

FIG. 10a is a schematic sectional side partial view of a chamber havinga recessed window with a mask and a magnetic field generator positionedto reduce the deposition of process residue on the window;

FIG. 10b is a schematic plan view of the window mask of FIG. 9a;

FIG. 11 is a schematic sectional side partial view of yet anotherversion of a chamber having a recessed window with a mask and anelectrical field generator positioned to reduce the deposition ofprocess residue on the window;

FIG. 12 is a graph showing the attenuation of radiation with processtime for a bare window, a recessed window with an overlying mask, and arecessed window with an overlying mask and adjacent magnets; and

FIG. 13 shows a reflected radiation signal trace after polarization ofthe radiation, rationing detected polarized radiation signals, andprocessing the ratioed signal through two cycles in a bandpass filter.

DESCRIPTION

The present invention is useful for monitoring processing of a substrate20, for example, to detect completion of a stage of processing of afeature 25 being processed on the substrate 20. For example, asillustrated in FIGS. 1a and 1 b, the substrate 20 may comprise anetch-resistant material 21 (resist), for example, a photoresist or hardmask layer, that is in a desired patterned configuration. Theetch-resistant material 21 overlies other materials 22, 24 which may beshaped as layers and which are formed on a wafer 26 of silicon, compoundsemiconductor or dielectric. The layers 22, 24 are stratums of thesubstrate 20 which may be composed of a single material or more than onematerial. During processing of the materials 22, 24, for example whenetching the materials, it may be desirable to stop processing uponapproaching or reaching an interface 23 between the first material 22and the second material 24 or after completion of processing one or bothof the first or second materials 22, 24. For example, when etching afeature 25, such as a via or trench in the substrate 20, it may bedesirable to stop or slow down the etching process upon reaching apredetermined depth of the first material 22 or after etching throughonly a small portion of the underlying second material 24. Although anetching process is provided to illustrate an exemplary application ofthe present invention, it should be understood that the invention mayalso be applied to materials formed during the deposition of material onthe substrate 20 or other processing methods.

The features 25 formed in a particular layer 22 on the substrate 20 mayalso have an orientation 33, such as a principal orientation, whichalong a primary direction. For example, the features 25 may be orientedin a principal orientation so that electrical signals may be moreexpeditiously passed therethrough. In other layers 35, formed above orbelow the layer 22 being etched, for example, as shown in FIG. 1b, thefeatures 36 may be oriented in other or second principal orientations 39that are different from the first principal orientation 33 of thefeatures 25 in the first layer 22. For example, the features 36 in thesecond layer 35 may be mostly oriented in a direction 39 that isperpendicular to the orientation 33, i.e., if the features 25 in thefirst layer 22 are oriented primarily along a 0° direction, then thefeatures 36 in the overlying second layer 35 may be mostly orientedalong a 90° orientation. For example, electrical interconnect lines onadjacent upper and lower levels which are oriented perpendicular to eachother reduce problems such as hot spots or excessiveinductance-capacitance (LC) crosstalk during operation, especially asthe frequency or speed of signal passing through is increased.

In one aspect of the present invention, processing of the substrate 20is monitored by monitoring an amplitude of the radiation reflected fromthe substrate, and enhancing the signal strength of the amplitudemodulation of radiation reflected from the features 25 relative to theintensity modulation of radiation reflected from the etch-resistantmaterial 21, by detecting substrate reflected radiation 31 having one ormore polarization angles. The polarization angle is the mode ofvibration of the radiation 31 in the plane perpendicular to thedirection of travel of the radiation. For example, FIG. 1a also showsradiation 31 having a plurality of polarization angles being reflectedfrom a feature 25 being etched and from the etch-resistant material 21on the substrate 20. The radiation 31 is polarized to one or morepolarization angles related to an orientation 33, for example, aprincipally orientation, of a feature 25 being processed on thesubstrate 20. For example, the radiation 31 may be polarized alongpolarization angles which are substantially parallel or perpendicular tothe principal orientation 33 of the feature 25. The polarization anglesmay include, for example, a first polarization angle P_(α) (0°) that issubstantially parallel to the principal orientation 33 and a secondpolarization angle P_(β) (90°) substantially perpendicular to theprincipal orientation 33.

Referring to FIG. 1a, the intensity of the feature reflected radiationcomponent I_(∥)(or p-component) having a first polarization angle thatis substantially parallel to, or directed along the length l of, theprincipal orientation 33 of the feature 25, has a larger magnitude thanfeature reflected radiation components which are at other polarizationangles relative to the principal orientation. For example, the radiationcomponent I₁₉₅ (or s-component) having a polarization angle that issubstantially parallel to the width w of the orientation 33 of thefeature 25, has a smaller magnitude than reflected radiation at otherpolarization angles. The measured I_(∥)and I₁₉₅ components may be usedto enhance the feature reflected component, from the equations:

I _(81 (sum)) =I _(81 (feature)) +I _(∥(resist))

I _(195 (sum)) =I _(⊥(feature)) +I _(⊥(resist))

The difference or summation of these equations allow separation of thefeature reflected component and the etch-resistant material reflectedcomponent, as follows:

ΔI=I _(⊥(sum)) −I _(∥(sum)) =I ^(⊥(feature)) −I _(∥(feature))

This occurs because the I^(∥(resist)) component is the same as theI_(⊥(resist)) component, and consequently, it cancels out from theequation, leaving behind only the feature reflected components. Thus,monitoring substrate reflected radiation at a plurality of polarizationangles can more accurately determine the intensity of the featurereflected components.

This phenomena may be explained with reference to FIGS. 2a and 2 b,which show that the vertical constructive/destructive phase interferencemay be defined using the ratio of the amplitude of the reflectedradiation to the amplitude of the incident radiation, the radiationbeing for example, light, in the equation

r _(sum)=(r ₁ +r ₂ *e ^(−iδ1))/(1+r ₁ *r ₂ *e ^(−iδ1)),

where

r ₁=(1−n ₁)/(1+n ₁); r ₂=(n ₁ −n ₂)/(n ₁ +n ₂);

and δ₁=4πn₁d₁/λ; and where n₁ and n₂ are the index of reflection of afeature in an oxide layer and the substrate, respectively, d₁ is thethickness of the oxide layer, and λ is wavelength. The lateralinterference effect is provided by

I _(r) =I ₀ |f _(pr) r _(pr) +e ^(−iδ) f _(feature) r _(feature)|²,

where f_(pr) is the percentage of photoresist covered area,

f_(feature) is the percentage of feature open area,

r _(1pr)=(r _(1p) +r ₂ *e ^(−iδ1)))/(1+r _(1p) *r ₂ *e ^(−iδ1))

where r_(1p)=(n_(p)−n₁)/(n_(p)+n₁)

r₂=(n₁−n₂)/(n₁+n₂), and

δ₁=4πn₁d_(feature)/λ

r _(pr)=(r _(p) +r _(1pr) *e ^(−iδ2))/(1+r _(p) *r _(1pr) *e ^(−iδ2)),

where r_(p)=(1−n_(p))/(1+n_(p)), and

δ₂=4πn_(p)d_(p)/λ, and

r _(feature)=(r ₁ +r ₂ *e ^(−iδ3))/(1+r ₁ *r ₂ *e ^(−iδ3))

where δ₃=4πn₁d₁/λ, and

δ₀=4πd₀/λ.

The intensity of the radiation reflected from the feature is given byI_(sum)=I₀|r_(sum)|². The complex frequency components due to thecombination of vertical and lateral interferences are, w_(pr)(photoresist component), w_(ox) (silicon dioxide component), w_(po)(difference between photoresist and silicon dioxide), w_(ox)−w_(pr),w_(ox)+w_(pr), w_(po)−w_(pr), w_(po)+w_(pr), w_(po)−w_(pr),w_(po)+w_(pr)+w_(ox), w_(ox)−w_(pr)−w_(po) and w_(ox)+w_(pr)−w_(po).However, a problem with the change in frequency components as a functionof amplitude arises because the shape of interference fringes isdistorted due to the coupling of the vertical and lateral interferenceeffects. For example, FIG. 3 shows the relative amplitude andfrequencies of the different frequency components w_(pr), w_(ox) andw_(po). Generally, the depth of etching a feature 25 in a substrate 20is related to the wavelength of the incident radiation by the equation,feature etch depth=wavelength/(2*IOR), where IOR is the index ofreflection of the incident radiation. As the etching depth of a feature25 being processed on a substrate 20 increases, the reflected radiationfrom the etched features 25 undergoes destructive/constructiveinterference to provide a detectable oscillating signal having a firstfrequency that is related to the etching rate and wavelength of theincident radiation. Meanwhile, the radiation reflected from theremaining surface of the substrate 20, which is etched at a differentetching rate, also undergoes destructive/constructive interference toprovide a detectable oscillating signal having a different and secondfrequency.

Detection of the modulations of the feature component is especiallydifficult when the substrate 20 has a small open area between theetch-resistant features 21 because the modulation of the resistcomponent from the larger area of the etch-resistant features 21dominates the modulation of the total signal. FIG. 4a shows a trace ofthe reflected radiation signal obtained during the etching of features25 comprising trenches having openings sized about 0.4 micron in asilicon dioxide dielectric layer on a substrate 20 having an open areaof at least about 20%. This trace of the summation signal comprises afirst stage (I) in which both the features 25 being etched and theresist material 21 which is also being partially removed, contribute thecomponents which interfere with one another and both contribute to thedetected oscillating modulated amplitude that changes unpredictably infrequency and shape. However, the second stage (II) which corresponds toetching of substantially only the etch-resistant material 21 (becausethe features 25 are fully etched) provides an amplitude trace having amore repeatable cyclic wavefront that is composed of mostly the resistcomponent. The endpoint of the etching process, lying between the twotraces and at a cumulative processing time of about 140 seconds, isdenoted by “Etching Endpoint”. When similar trace studies were conductedfor a substrate 20 having a smaller fraction of open area, for example,an open area of 5%, as shown in FIG. 4b, the detected reflectedradiation provided a signal trace having a cyclic and repeatablewaveform that is mostly the signal intensity of the resist componentthat is reflected from the surface of the etch-resistant material 21which occupies more than 95% of the area of the substrate 20. Thereflected radiation from the relatively small open area of the features25 on the substrate 20 that were being etched had a much smallerrelative signal intensity that is lost in the larger resist componentsignal.

It was also determined that the intensity of summation signal is alsodependent upon the size of the features 25 being etched in the substrate20. FIGS. 5a and 5 b show amplitude traces obtained during the etchingof 0.4 micron and 1 micron features in silicon dioxide on polysiliconover a silicon substrate 20, respectively, both substrates having thesame open area of 30%. Again, the first stages, corresponding to etchingof both overlying etch-resistant material 21 and the silicon dioxide,provided a summation amplitude trace having complex and variable shape;whereas, the second stages, corresponding to etching of substantiallyonly residual resist, provided a summation amplitude trace having arepeatable and cyclic waveform.

FIG. 6 shows the relationship between the quality of the summationsignal in relation to the size of the features 25 being processed oretched in the substrate 20 and as a function of the exposed area ofsilicon dioxide on the substrate 20. There are two regimes, one in whichintensity of summation signal is acceptable, and the other in which thesummation signal intensity is not acceptable. The etching feature window41 denotes a typical region of etched feature size and substrate openarea in which many current trench features are processed. Thus,conventional process monitoring methods only allow a small window regionof the reflected radiation to be analyzed when the feature size or openarea on the substrate becomes small.

In another aspect of the present invention, a filter 53 may be used toselectively filter a signal generated by the radiation detector 54 inrelation to a detected intensity of the reflected radiation. In oneversion, the filter 53 is a bandpass filter that increases the relativeintensity of a selected passband of frequencies in relation to theintensity of other frequency components of the reflected radiation. Forexample, the bandpass filter 53 may be adapted to filter the incomingsignal from the radiation detector 54 to pass through a band offrequencies that are related to a frequency of a radiation that isreflected from a feature 25 being processed on the substrate 20, whilereducing the intensity of the signal that arises from radiation that isnot reflected from the features 25 being processed on the substrate 20.The type of bandpass filter 53 used depends upon the intended processuse and the passband frequency limits. In one version, the bandpassfilter 53 is an electrical signal processor that operates by filteringthe signal and selectively passing thorough only a passband offrequencies. The electrical signal processor may be a digital signalprocessor that digitizes a radiation signal received from a radiationdetector, and filters the digitized signal.

In one version, the selected frequency is approximately the centralfrequency of the passband. For example, if the bandpass filter has apassband ranging from A to B Hz, the center frequency is (A+B)/2 Hz.When the passband frequency range is centered about a selected frequencyof the destructive/constructive interference signals obtained from theradiation component that is reflected from the etched features 25,thereby dampening or excluding the destructive/constructive signal thatarises from the radiation component that is reflected from the remainingsurface of the substrate 20, for example, a patterned etch-resistantmaterial on the substrate 20. However, the selected frequency does nothave to be the center frequency of the passband. That is, comparableresults can be achieved by selecting with other frequencies within thepassband. In one example, the passband frequency range includesfrequencies that are within about +_(—)10% of a selected frequency of aradiation component that is reflected from the substrate 20. Forexample, for trench shaped features 25 being etched in a dielectricmaterial on a substrate 20, a suitable frequency is from about 0.09 Hzto about 0.11 Hz, for an oxide etch rate of about 5000 angstroms/min.

In one version, the passband frequency range may be selected to providea coherence length of a non-coherent radiation source 58, which may be,for example, a plasma emission having multiple wavelengths and phases.The coherence length is the length in which interference effects ofradiation from the radiation source 58 may be observed. For anon-coherent radiation source, the coherence length is related to theequation λ²/nΔλ, where n is the index of refraction of the layer 22being etched, λ is the wavelength at the center of the plasma emissionspectrum, and Δλ is the wavelength range, and hence the frequency range,passed by the bandpass filter. The coherence length may be obtained whenΔλ is chosen such that λ²/Δλ is greater than the thickness of the layer22 being etched. In one version, the Δλ of the bandpass filter 53 may be1.5 nanometers for a plasma emission centered about 254 nanometers.

The reflected radiation signal may also be processed in one or morecycles through the bandpass filter 53, so that in each cycle, the signalis filtered to pass through the component of the radiation signalcorresponding to the frequencies of reflected radiation from the etchedfeatures 25, while dampening the radiation signal corresponding to thefrequencies of the reflected radiation from the other or resist 21portions of the substrate 20. For example, during an etching process, ineach pass, the bandpass filter 53 would increase the signal strength ofthe radiation reflected from the etched features 25 relative to thesignal strength of the radiation reflected from the remaining substratesurface. A suitable number of cycles is from about 1 to about 10 cycles,and more typically from about 2 to about 5 cycles.

FIG. 7 shows a graph with the frequency response (%) versus normalizedfrequency for multiple passes through the bandpass filter 53 showing theincrease in strength of radiation having frequencies centered about theetched feature component relative to, for example, the resist componentor the rotating magnetic field component that is used during processing.As the number of passes were increased from 1 to 2, the resultantreduction in amplitude of the non-feature reflected radiation componentenhanced the signal to noise ratio of the reflected radiation signalfrom the feature in relation to the other signals from the othersurfaces of the substrate.

The present invention is useful for etching a substrate 20 in anapparatus 27, as for example, schematically illustrated in FIG. 8a andFIG. 8b. Generally, the apparatus 27 comprises a chamber 35 having asupport 32 for receiving a substrate 20 in a process zone 30. Processgas may be introduced into the chamber 35 through a gas supply 34comprising a gas source 36, gas inlets 38 located around the peripheryof the substrate 20 (as shown) or in a showerhead mounted on the ceilingof the chamber (not shown). A gas flow controller 40 may be used tocontrol the flow rate of the process gas. Spent process gas and etchantbyproducts are exhausted from the chamber 35 through a gas exhaust 42comprising roughing and turbomolecular pumps (not shown) and a throttlevalve 44 which may be used to control the pressure of process gas in thechamber 35.

An energized gas or plasma is generated from the process gas by a gasenergizer 46 that couples electromagnetic energy to the process gas inthe process zone 30 of the chamber 35. For example, a first processelectrode 55, such as a sidewall of the chamber 35 and a secondelectrode 52, such as an electrically conducting portion of the support32 below the substrate 20 may be used to further energize the gas in thechamber 35, as shown in FIG. 8a. The first and second electrodes 52, 55are electrically biased relative to one another by an RF voltageprovided by an electrode voltage supply 62. The frequency of the RFvoltage applied to the electrodes 52, 55 is typically from about 50 KHzto about 60 MHz. As another example, the gas energizer 46 may comprisean inductor coil 47 which inductively couples electromagnetic energy tothe gas in the chamber 35, as shown in FIG. 8b.

The radiation 31 incident on the substrate 20 may be provided by aradiation source 58, which may be, for example, a plasma inside oroutside the chamber, radiation lamp, LED or laser. The radiation source58 may provide radiation such as ultraviolet (UV), visible or infraredradiation; or it may provide other types of radiation such as X-rays.The radiation source 58 may comprise, for example, an emission from aplasma generated inside the chamber 28 which is generally multispectralwith multiple wavelengths extending across a spectrum, as shown in FIG.8a, and also generally non-coherent, i.e., with multiple phases. Theradiation source 58 may also be positioned outside the chamber 35 sothat the radiation 31 may be transmitted from the source 58 through awindow 130 and into the chamber 35, as shown in FIG. 8b. The radiationsource 58 may also provide radiation having predominant characteristicwavelengths, for example, a single wavelength, such as monochromaticlight, as provided by a He-Ne or Nd-YAG laser. The laser source alsoprovides coherent light with a predominant or single phase.Alternatively, the radiation source 58 may comprises a lamp thatprovides a radiation emission having multiple wavelengths, such aspolychromatic light, which may be selectively filtered to a singlewavelength. Suitable radiation sources 58 for providing polychromaticlight include Hg discharge lamps that generate a polychromatic lightspectrum having wavelengths in a range of from about 180 to about 600nanometers; arc lamps such as xenon or Hg-Xe lamps and tungsten-halogenlamps; and light emitting diodes (LED).

In one version, a non-polarized radiation source 58 that provides asource of non=polarized light, such as ultraviolet, infrared or visiblelight, is used. The non-polarized source is useful when polarizedradiation is preferentially absorbed during the process, by for example,the energized gas or plasma or a residue that accumulates on the chamberwindow. The polarization state also influences the radiation absorptioncharacteristics in materials having oriented crystalline structures,such as crystals having other than cubic symmetry.

A normal incidence of the radiation onto the substrate 20 may also beused to accurately detect processing endpoints for a substrate 20 havingtall and narrowly spaced features, for example, the etch-resistantfeatures, over the layers 22, 24. The normal incident radiation is notblocked from reaching the layers 22, 24 by the height of theetch-resistant material features. However, it should be understood thatnormal incidence is not necessary for detection of the reflectedradiation and that other angles of incidence may be employed.

The radiation may be polarized to a plurality of polarization angles byplacing first and second radiation polarizers 59 a, 59 b in theradiation pathway incident upon and reflected back by the substrate 20.While the present example shows the first and second radiationpolarizers 59 a, 59 b in the pathway of radiation that is incident uponthe substrate 20, they can also be in the pathway reflected back by thesubstrate 20, or they can be part of the radiation detector 54. Thefirst polarizer 59 a selectively pass radiation that is oriented at afirst polarization angle and the second polarizer 59 b selectivelypasses radiation oriented at a second polarization angle. The first andsecond polarizers 59 a,b may be a single structure or more than onestructure. In one version, the polarizers 59 a,b comprise radiationpermeable material coated with one or more thin films that selectivelypolarize the radiation passing through the material, or in anotherversion, they may be a rotatable filter. When a rotating polarizer 59a,b is used, the radiation is sampled at periodic intervals to obtainonly the reflected radiation signal components that are related to thefeature angle orientation.

One or more radiation detectors 54 are used to detect the radiation 31reflected by the substrate 20. The radiation detectors 54 may comprise aradiation sensor, such as a photovoltaic cell, photodiode,photomultiplier, or phototransistor. The radiation detector 54 providesan electrical output signal in response to a measured intensity of thereflected radiation which may comprise a change in the level of acurrent passing through an electrical component or a change in a voltageapplied across an electrical component. A plurality of radiationdetectors 54 may also be used (not shown) with each detector set tocapture radiation having a different polarization angle. The detectorsignals are evaluated to separate the reflected radiation signals fromthe features 25 and the etch-resistant material 21 reflected radiationcomponents by a controller 100. The controller 100 can also be adaptedto evaluate the detected signal to determine the magnitude of radiationhaving different polarization angles.

The substrate reflected radiation may be detected at a small incidentangle or along a substantially vertical direction. The verticaldetection angle allows more accurate monitoring of features 25 beingprocessed in the chamber 35, for example, to determine a depth ofetching of the features 25 or a depth of material deposited into afeature 25 or as a layer on the substrate 20. The vertical angle isespecially desirable when the features 25 being etched have high aspectratios, and it is difficult for radiation directed at a small incident(or reflected) angle to penetrate the depth of the feature 25 withoutbeing blocked by sidewalls of the feature 25 or the sidewalls of thepatterned etch-resistant material 21. The vertical detection angle maybe obtained by positioning the radiation detector 54, and optionally theradiation source 58 (other than a plasma source which is already abovethe substrate 20), vertically above the substrate 20.

The chamber 35 may be operated by a controller 100 that executes acomputer-readable process control program 102 on a computer system 104comprising a central processor unit (CPU) 106, such as for example a68040 microprocessor, commercially available from Synergy Microsystems,California, or a Pentium Processor commercially available from IntelCorporation, Santa Clara, Calif., that is coupled to a memory 108 andperipheral computer components. The memory 108 comprises acomputer-readable medium having the computer-readable program 102embodied therein. Preferably, the memory 108 includes a hard disk drive110, a floppy disk drive 112, and random access memory 114. The computersystem 104 further comprises a plurality of interface cards including,for example, analog and digital input and output boards, interfaceboards, and motor controller boards. The interface between an operatorand the controller 110 can be, for example, via a display 118 and alight pen 120. The light pen 120 detects light emitted by the monitor118 with a light sensor in the tip of the light pen 120. To select aparticular screen or function, the operator touches a designated area ofa screen on the monitor 118 and pushes the button on the light pen 120.Typically, the area touched changes color, or a new menu is displayed,confirming communication between the user and the controller 110.

Computer-readable programs such as those stored on other memoryincluding, for example, a floppy disk or other computer program productinserted in a floppy disk drive 112 or other appropriate drive, orstored on the hard drive, may also be used to operate the controller100. The process control program 102 generally comprises process controlsoftware 124 comprising program code to operate the chamber 28 and itscomponents, process monitoring software 126 to monitor the processesbeing performed in the chamber 28, safety systems software, and othercontrol software. The computer-readable program 102 may be written inany conventional computer-readable programming language, such as forexample, assembly language, C⁺⁺, Pascal, or Fortran. Suitable programcode is entered into a single file, or multiple files, using aconventional text editor and stored or embodied in computer-usablemedium of the memory 108 of the computer system. If the entered codetext is in a high level language, the code is compiled, and theresultant compiler code is then linked with an object code ofprecompiled library routines. To execute the linked, compiled objectcode, the user invokes the object code, causing the CPU 106 to read andexecute the code to perform the tasks identified in the program.

FIG. 9 is an illustrative block diagram of a hierarchical controlstructure of a specific embodiment of a process control program 102according to the present invention. Using a light pen interface, a userenters a process set and chamber number into a process selector program132 in response to menus or screens displayed on the CRT terminal. Theprocess chamber program 124 includes program code to set the timing, gascomposition, gas flow rates, chamber pressure, RF power levels, supportposition and other parameters of a particular process. The process setsare predetermined groups of process parameters necessary to carry outspecified processes. The process parameters are process conditions,including without limitations, gas composition, gas flow rates,pressure, and gas energizer settings. In addition, parameters needed tooperate the process monitoring program 126 are also inputted by a userinto the process selector program. These parameters include knownproperties of the materials being processed, especially radiationabsorption and reflection properties, such as reflectance and extinctioncoefficients; process monitoring algorithms that are modeled fromempirically determined data; tables of empirically determined orcalculated values that may be used to monitor the process; andproperties of materials being processed on the substrate.

The process sequencer program 134 comprises program code to accept achamber type and set of process parameters from the process selectorprogram 132 and to control its operation. The sequencer program 134initiates execution of the process set by passing the particular processparameters to a chamber manager program 136 that controls multipleprocessing tasks in the process chamber 28. Typically, the processchamber program 124 includes a substrate positioning program 138, a gasflow control program 140, a gas pressure control program 142, a gasenergizer control program 144 and a heater control program 146.Typically, the substrate positioning program 138 comprises program codefor controlling chamber components that are used to load the substrate20 onto the support 32 and optionally, to lift the substrate 20 to adesired height in the chamber 35 to control the spacing between thesubstrate 20 and the gas inlets 38 of the gas delivery system 34 theprocess gas control program 140 has program code for controlling theflow rates of different constituents of the process gas. The process gascontrol program 140 controls the open/close position of the safetyshut-off valves, and also ramps up/down the gas flow controller 40 toobtain the desired gas flow rate. The pressure control program 142comprises program code for controlling the pressure in the chamber 28 byregulating the aperture size of the throttle valve 44 in the gas exhaust42 of the chamber. The gas energizer control program 144 comprisesprogram code for setting low and high-frequency RF power levels appliedto the process electrodes 52, 55 in the chamber 35. Optionally, theheater control program 146 comprises program code for controlling thetemperature of a heater element (not shown) used to resistively heat thesupport 32 and substrate 20.

The process monitoring program 126 may comprise program code to obtainsample or reference signals from the radiation source 58, radiationdetector 54, or controller 100 and processes the signal according topreprogrammed criteria. Typically, a radiation amplitude or spectrumtrace is provided to the controller 100 by an analog to digitalconverter board in the radiation detector 54. The process monitoringprogram 126 may also send instructions to the controller 100 to operatecomponents such as the radiation source 58, radiation detector 54 andother components. The program may also send instructions to the chambermanager program 136 or other programs to change the process conditionsor other chamber settings.

The process monitoring program 126 may also comprise program code toobtain and evaluate signals from the radiation detector 54. The programcode may be designed to reduce the intensity of undesirable frequencycomponents of the reflected radiation, for example, the frequencycomponents that arise from radiation that is not reflected from thefeatures 25 being processed on the substrate 20. For example, thebandpass filter may be adapted to filter an incoming radiation signalfrom the detector 54 to obtain a frequency band centered about one ormore selected frequencies of the radiation reflected from the substrate20.

To define the parameters of the process monitoring program 126,initially, one or more substrates 20 having predetermined thicknesses ofmaterial are selected for processing. Each substrate 20 is placed at onetime into the process chamber 35 and process conditions are set toprocess a material 22 or an underlying material 24 on the substrate 20.Radiation reflected from the substrate and/or emitted from the plasma inthe chamber are monitored using one or more radiation detectors 54.After a series of such traces are developed, they are examined toidentify a recognizable change in a property of the trace, which is usedas input for the computer program, in the form of an algorithm, a tableof values, or other criteria for suitable for evaluating an event in thechamber 35 or a property of the substrate 20. For example, the processmonitoring program 126 may include program code to evaluate a signalcorresponding to an intensity of reflected radiation which may be usedto detect both an onset and completion of processing of the substrate20. As another example, the computer program 126 comprises program codeto evaluate first and second signals that correspond to radiationemitted from the plasma and/or reflected from the substrate 20.

Thus, the process monitoring program 126 may comprise program code toanalyze an incoming signal trace provided by the radiation detector 54and determine a process endpoint or completion of a process stage when adesired set of criteria is reached, such as when an attribute of thedetected signal is substantially similar to a pre-programmed value. Theprocess monitoring program 126 may also be used to detect a property ofa material being processed on the substrate such as a thickness, orother properties, for example, the crystalline nature, microstructure,porosity, electrical, chemical and compositional characteristics of thematerial on the substrate 20. The computer program 126 may also beprogrammed to detect both an onset and completion of processing of thesubstrate 20, for example, by detecting a change in amplitude or a rateof change of amplitude of the radiation 31. The desired criteria areprogrammed into process monitoring program 126 as preset or storedparameters and algorithms. The program 126 may also include program codefor modeling a trace of radiation, selecting a feature from the modeledtrace or allowing a user to select the feature, storing the modeledtrace or the feature, detecting a portion of an incoming signal from aradiation detector 54, evaluating the measured signal relative to thestored trace or feature, and calling an end of a process stage of theprocess being performed on the substrate 20 or displaying a measuredproperty of a material on the substrate 20.

In one version, the process monitoring software comprises program codefor continuously analyzing a trace of a measured amplitude of reflectedradiation by drawing a box or “window” around the end portion of thetrace and back in time, with signal height and time length establishedin the preprogrammed algorithm. A set of windows may be programmed todetect a valley or peak in the trace of the reflected intensity, triggeron an upward slope to detect a later endpoint, or to trigger on adownward slope to detect an endpoint before a valley in the trace. Thefirst criterion is met when the signal in the trace becomes too steepand exits or moves out of the preprogrammed box (“WINDOW OUT”) or whenSit becomes gradual and enters the box (“WINDOW IN”). Additional windowsare sequentially applied on the moving trace to generate the completeset of criteria to make a determination on whether the change in signalmeasured in the real time trace is an endpoint of the process, such asan onset or completion of the process, a change in the property of thematerial, or is only noise. The direction of entering or exiting a boxmay also be specified as part of the preprogrammed input criteria foroperating the process monitoring program 126. Upon detecting an onset orcompletion of a process, the process monitoring program signals theprocess chamber program 126 which sends instructions to the controller100 to change a process condition in a chamber 35 in which the substrate20 is being processed. The controller 100 is adapted to control one ormore of the gas supply 34, gas energizer 46, or throttle valve 44 tochange a process condition in the chamber 35 in relation to the receivedsignal.

The data signals received by and/or evaluated by the controller 100 maybe sent to a factory automation host computer 300. The factoryautomation host computer 300 may comprise a host software program 302that evaluates data from several systems 27, platforms or chambers 35,and for batches of substrates 20 or over an extended period of time, toidentify statistical process control parameters of (i) the processesconducted on the substrates 20, (ii) a property that may vary in astatistical relationship across a single substrate 20, or (iii) aproperty that may vary in a statistical relationship across a batch ofsubstrates 20. The host software program 302 may also use the data forongoing in-situ process evaluations or for the control of other processparameters. A suitable host software program comprises a WORKSTREAM™software program available from aforementioned Applied Materials. Thefactory automation host computer 300 may be further adapted to provideinstruction signals to (i) remove particular substrates 20 from theprocessing sequence, for example, if a substrate property is inadequateor does not fall within a statistically determined range of values, orif a process parameter deviates from an acceptable range; (ii) endprocessing in a particular chamber 35, or (iii) adjust processconditions upon a determination of an unsuitable property of thesubstrate 20 or process parameter. The factory automation host computer300 may also provide the instruction signal at the beginning or end ofprocessing of the substrate 20 in response to evaluation of the data bythe host software program 302.

It was further discovered that the signal to noise ratio of thereflected radiation signal could be further improved by placing a window130 through which the radiation detector 54 views radiation reflectedoff the substrate in a recess 61 in the wall of the chamber 35. FIG. 10ais a schematic sectional side view of a chamber having a window 130 in arecess in the wall 51 of the chamber 35, a detector 54 to detect theradiation reflected from the substrate and passing through the window130 and generate a signal in response to the detected radiation, and acontroller 100 to evaluate the detected signal to monitor the process.The window 130 comprises a material that is permeable to the wavelengthsof radiation that are monitored by the controller 100. For infrared,visible, and UV radiation, the window 130 may be made of a ceramic, suchas for example, one or more of Al₂O₃, Si, SiO₂, TiO₂, ZrO₂ or mixturesand compounds thereof. The ceramic may also comprise a monocrystallinematerial, such as for example, sapphire which is monocrystalline aluminaand that exhibits good erosion resistance to halogen plasmas, especiallyfluorine containing plasmas.

The recess 61 in the wall 51 of the chamber 35 is shaped and sized toreceive a mask 140 therein, as shown in FIG. 10. For example, when themask 140 is cylindrical in shape, the recess 61 may also becylindrically shaped. The mask 140 is sized to substantially cover thewindow 130 thereby reducing or preventing the deposition of processresidues on the window 130. The mask 140 may be made of a material thatis resistant to erosion by the process gas or plasma in the chamber 35,such as a plasma resistant material, for example, one or more of Al₂O₃,SiO₂, AlN, BN, Si, SiC, Si₃N₄, TiO₂, ZrO₂, or mixtures and compoundsthereof.

The mask 140 comprises one or more apertures 145 therein, as shown inFIG. 10b. The apertures 145 are shaped and sized to reduce thedeposition of process residues therein while allowing a sufficientamount of radiation to pass therethrough to operate the controller 100.For example, the apertures 145 may be shaped and sized to pass bothincident and reflected radiation beams therethrough—for interferometricor ellipsometric analysis—or it may be shaped and sized to monitor aspectral emission from the plasma for plasma emission analysis. It isbelieved that the apertures 145 reduces the deposition of processresidues therein by reducing the access of neutral gaseous species(which are often the residue forming species) or by allowing highlyenergized gaseous ions to etch away process residues that form on thewalls of the apertures 145. The aspect ratio and depth of the recess 145generally control the distance that must be traveled by the energeticgaseous species before they reach the internal surfaces of the recess145 for example, a window 130 in the recess 145. Suitable apertures 145comprises an aspect ratio of at least about 0.25:1 and the aspect ratiomay also be less than about 12:1. In one version, the apertures 145comprises an opening size of from about 0.1 to about 50 mm and a depthof from about 0.5 to about 500 mm. The mask 140 may also comprise aplurality of apertures 145, such as for example, a plurality ofhexagonal or circular shaped holes.

An electromagnetic field source may be adapted to maintain anelectromagnetic field about the window 130. The electromagnetic fieldsource comprises an electrical or magnetic field source. Theelectromagnetic field applied about the wall 51 may reduce thedeposition of process residues on the window 130 in the recess 61 in thewall. For example, in the embodiment shown in FIG. 10a, theelectromagnetic field source comprises a magnetic field source 195adapted to maintain a magnetic field near the portion of the wall 51,about the recess 61, or across the window 130. The magnetic field source195 comprises at least one magnet 200 or electromagnet (not shown) thatis positioned adjacent or abutting the recess, wall or window 130 toprovide magnetic energy thereabout. For example, in one version, themagnetic energy may be confined to the space around the recess 61 orwindow 130 and may penetrate only a small distance into the chamber 35.In this version, the magnetic field source 195 provides a magnetic fieldthat is preferentially concentrated across the recess 61 or window 130relative to other portions of the chamber 35. Generally, a suitablemagnetic field strength may be from about 10 to about 10,000 Gauss, andmore preferably from about 50 to about 2000 Gauss, but the actualmagnetic strength selected would depend upon the window size, energy ofthe plasma ions, and other factors. In the embodiment illustrated inFIG. 10a, the magnetic field source 195 comprises a plurality ofmagnetic poles 200 disposed about a perimeter of the recess in the walland having opposing magnetic polarities

In another embodiment, as illustrated in FIG. 11, the electromagneticfield source comprises an electrical field source 220 that provideselectrical energy about the wall 51, recess 61 or across the window 130(as shown) to maintain an electrical field thereabout. It is believedthat the electrical field reduces the deposition of process residues onthe wall 51, in the recess 61, or on the window 130, for example, byrepelling the charged residue forming species or by causing theenergized gaseous species to bombard the window 130 to etch away theprocess residues. The electric field source 220 may comprise anelectrode 225 that is adjacent to, abutting, or behind the wall 51,about the recess 61, or near the window 130, to couple electrical energythereabout. The electrical field may be adapted to have electrical fieldcomponents which are parallel or perpendicular to the plane of the wall51 or window 130. The electrode 225 may be sized sufficiently large toprovide an electric field that covers an entire area of the wall 51 orthe window 130. The electrode 225 may also comprise eddy currentreducing slots that are shaped and sized to reduce any eddy currentsthat may be induced in the electrode 225. A voltage source 245electrically biases the electrode 225 with a DC, AC or RF voltage,typically of from about 10 to about 10,000 volts, and more preferablyfrom about 20 to about 4000 volts. 35FIG. 12 shows the attenuation ofradiation over processing time for a bare window, a recessed window 130,and a recessed window 130 with an adjacent magnet 200. It can be seenthat radiation passing through a bare, unrecessed window lacking anelectromagnetic field source reaches the maximum acceptable attenuationat less than 40 plasma process hours. In comparison, radiation passingthrough a recessed window 130 reaches the maximum acceptable attenuationin around 100 hours and the radiation passing through a recessed window130 comprising an adjacent magnet 200 reaches a maximum acceptableattenuation after 100 hours. This data shows that a recessed window 130provides a substantial reduction in the attenuation of the radiationintensity during a plasma process. Adding an electromagnetic fieldsource, in this case an adjacent magnet 200, substantially enhances thisreduction in attenuation.

EXAMPLE

The following example demonstrates the effectiveness of the presentinvention. However, the present invention may be used in other processesand for other uses as would be apparent to those of ordinary skill inthe art and the invention should not be limited to the examples providedherein. In this example, features 25 were etched in a substrate 20 in amagnetically enhanced etching chamber with a recessed window covered bya mask and having a magnetic field generator about the window, as forexample illustrated in FIG. 10a. The substrate 20 being etched was asilicon wafer comprising a dielectric layer 22 comprising a 1 micronsilicon dioxide layer, a 0.1 micron silicon nitride layer, and a 1micron silicon dioxide layer. An overlying patterned photoresist layer21 covered the dielectric layer 22. The dielectric layer 22 was etchedusing a process gas comprising 40 sccm CHF₃, 20 sccm CF₄, and 50 sccmAr. The pressure in the chamber was maintained at 200 mTorr, the processelectrode R.F. bias power level at 1300 watts, and portions of thechamber were maintained at temperatures of about 15° C. The etchedfeatures 25 had openings sized from about 0.4 micron to about 1 micron,the exposed dielectric (silicon dioxide) area on the silicon wafer wasfrom about 5% to about 50%.

In this example, the radiation reflected from the substrate 20 wasdetected in two polarization angles, and a bandpass filter was used toevaluate the signal generated from the radiation detector. The first andsecond radiation detectors were used to detect and measure thep-component and s-component of the polarized radiation. The radiationincident upon the substrate 20 comprised radiation having a wavelengthof 254 nm. A passband filter placed in the radiation path was adapted toselectively pass thorough radiation having frequencies within a passbandrange that was centered about the radiation frequency reflected from thefeatures 25 being etched in the substrate 20.

FIG. 13 shows a signal trace obtained after polarization of theradiation, rationing the detected polarized radiation signals, andprocessing the ratioed signal through two cycles in a bandpass filter.The incident radiation had a wavelength of 254 nm. The ratio of theradiation reflected from the features 25 and the etch-resistant material21 and was determined. The ratioed signal trace was processed throughtwo cycles of a bandpass filter. For a substrate having an open oxidearea of 50%, the predicted etch depth was identical to the measured etchdepth, both at about 0.46 micron. When the same tests were conducted ona substrate having an open oxide area of 30%, the predicted etch depthat 0.49 micron was slightly different from the measured etch depth was0.5 micron; and for an open oxide area of 20%, the predicted etch depthwas 0.46 micron for a measured etch depth of 0.48 micron. These resultsdemonstrate the accuracy of the present method and apparatus.

The present invention is described with reference to certain preferredversions thereof, however, other versions are possible. For example, theendpoint detection process can be used for detecting endpoints in otherprocesses and in other chambers as would be apparent to one of ordinaryskill, including without limitation, other types of etching chambers,including but not limited to, capacitively coupled chambers, ionimplantation chambers, and deposition chambers such as PVD or CVDchambers. Therefore, the spirit and scope of the appended claims shouldnot be limited to the description of the preferred versions containedherein.

What is claimed is:
 1. A substrate processing apparatus comprising: achamber capable of processing a substrate; a radiation source to providea radiation; a radiation polarizer adapted to polarize the radiation toone or more polarization angles that are selected in relation to anorientation of a feature being processed on the substrate; a radiationdetector to detect radiation reflected from the substrate duringprocessing and generate a signal; and a controller to process thesignal.
 2. An apparatus according to claim 1 wherein the radiation ispolarized to a plurality of polarization angles.
 3. An apparatusaccording to claim 1 wherein the radiation is polarized to apolarization angle that is substantially parallel, or substantiallyperpendicular, to the orientation of the feature.
 4. An apparatusaccording to claim 1 wherein the feature comprises a principalorientation, and wherein the radiation is polarized to a firstpolarization angle substantially parallel to the principal orientationand a second polarization angle substantially perpendicular to theprincipal orientation.
 5. An apparatus according to claim 1 wherein thecontroller processes the signal to increase the intensity of a signalcomponent arising from the radiation reflected by the feature beingprocessed in the substrate relative to other signal components.
 6. Anapparatus according to claim 1 wherein the controller processes signalcomponents of reflected radiation that are polarized at differentpolarization angles.
 7. An apparatus according to claim 6 wherein thecontroller determines a ratio or subtraction product of the reflectedradiation signal components.
 8. An apparatus according to claim 7wherein the reflected radiation signal components comprise signalcomponents arising from radiation polarized at polarization angles whichare substantially parallel, or substantially perpendicular, to theorientation of the feature.
 9. An apparatus according to claim 1 whereinthe radiation polarizer comprises one or more polarizing filters.
 10. Anapparatus according to claim 1 wherein the controller comprises abandpass filter.
 11. An apparatus according to claim 10 wherein thebandpass filter increases the intensity of a signal component arisingfrom the radiation reflected by the feature being processed in thesubstrate relative to other signal components.
 12. An apparatusaccording to claim 10 wherein the bandpass filter selectively passesthrough signal frequencies within a frequency passband that is selectedin relation to a intensity modulation frequency of radiation reflectedfrom the feature being processed on the substrate.
 13. An apparatusaccording to claim 12 wherein the frequency passband is centered aboutthe modulation frequency.
 14. An apparatus according to claim 1 wherein:the chamber comprises a substrate support, gas supply, gas energizer,and gas exhaust; and the controller analyzes the signal to detect anattribute in the signal related to a process endpoint, the attributecomprising a valley, peak, upward slope or downward slope, in thesignal; and the controller operates one or more of the substratesupport, gas supply, gas energizer, and gas exhaust, to change a processcondition upon detection of the signal attribute.
 15. A method ofprocessing a substrate in a process zone, the method comprising thesteps of: (a) providing a substrate in the process zone; (b) settingprocess conditions to process the substrate with an energized gas; (c)providing radiation that is polarized at one or more polarization anglesthat are selected in relation to an orientation of a feature beingprocessed on the substrate; (d) detecting radiation reflected from thesubstrate and generating a signal in response to the detected radiation;and (e) processing the signal.
 16. A method according to claim 15wherein in (c) the radiation is polarized at a plurality of polarizationangles.
 17. A method according to claim 15 wherein in (c) the one ormore polarization angles comprise a polarization angle is substantiallyparallel, or substantially perpendicular, to the orientation of thefeature.
 18. A method according to claim 15 wherein in (c) the one ormore polarization angles comprise a first polarization anglesubstantially parallel to the feature orientation and a secondpolarization angle substantially perpendicular to the featureorientation.
 19. A method according to claim 15 wherein the feature is atrench having a principal orientation, and wherein in (c) the one ormore polarization angles comprise a polarization angle is related to theprincipal orientation of the trench.
 20. A method according to claim 19wherein (e) comprises determining a depth of the trench.
 21. A methodaccording to claim 15 wherein (e) comprises increasing the intensity ofa signal component that arises from the radiation reflected by a featurebeing processed in the substrate relative to other signal components.22. A method according to claim 21 comprising processing signalcomponents of reflected radiation that are polarized at differentpolarization angles.
 23. A method according to claim 22 comprisingdetermining a ratio or subtraction product of the reflected radiationsignal components.
 24. A method according to claim 22 wherein thereflected radiation signal components comprises signal componentsarising from radiation polarized at polarization angles which aresubstantially parallel, or substantially perpendicular, to theorientation of the feature.
 25. A method according to claim 15 wherein(c) comprises increasing the intensity of a signal component arisingfrom the radiation reflected by the feature being processed in thesubstrate relative to other signal components.
 26. A method according toclaim 25 wherein (c) comprising filtering the signal to selectively passthrough a frequency passband relating to an intensity modulationfrequency of the radiation reflected from the feature being processed onthe substrate.
 27. A method according to claim 26 wherein the frequencypassband is centered about the modulation frequency.
 28. A methodaccording to claim 15 wherein (e) comprises analyzing the signal todetect an attribute in the signal related to a process endpoint, theattribute comprising a valley, peak, upward slope, or downward slope, inthe signal, and wherein the method further comprises: changing a processcondition upon detection of the signal attribute.
 29. A substrateprocessing apparatus comprising: a chamber capable of processing asubstrate; a radiation source to provide a radiation; a radiationpolarizer adapted to polarize the radiation to a plurality ofpolarization angles; a radiation detector to detect radiation reflectedfrom the substrate during processing and generate a signal; and acontroller to process the signal.
 30. An apparatus according to claim 29wherein the plurality of polarization angles are selected in relation toa principal orientation of a feature being processed on the substrate.31. An apparatus according to claim 30 wherein the plurality ofpolarization angles are substantially parallel or substantiallyperpendicular to the principal orientation.
 32. An apparatus accordingto claim 29 wherein the controller processes signal components ofreflected radiation that are polarized at the plurality of polarizationangles.
 33. An apparatus according to claim 32 wherein the controllerdetermines a ratio or subtraction product of the reflected radiationsignal components.
 34. An apparatus according to claim 29 wherein thecontroller comprises a bandpass filter to selectively passes throughsignal frequencies within a frequency passband that is selected inrelation to an intensity modulation frequency of radiation reflectedfrom a feature being processed on the substrate.
 35. An apparatusaccording to claim 34 wherein the frequency passband is centered aboutthe modulation frequency.
 36. A method of processing a substrate in aprocess zone, the method comprising the steps of: (a) providing asubstrate in the process zone; (b) setting process conditions to processa feature on the substrate with an energized gas; (c) providingradiation that is polarized to a plurality of polarization angles; (d)detecting radiation reflected from the substrate and generating a signalin response to the detected radiation; and (e) processing the signal.37. A method according to claim 36 wherein in (c) the plurality ofpolarization angles are selected in relation to an orientation of afeature being processed on the substrate.
 38. A method according toclaim 37 wherein the plurality of polarization angles comprise apolarization angle that is substantially parallel, or substantiallyperpendicular, to the feature orientation.
 39. A method according toclaim 37 wherein plurality of polarization angles comprise a firstpolarization angle substantially parallel to the feature orientation anda second polarization angle substantially perpendicular to the featureorientation.
 40. A method according to claim 36 wherein (e) comprisesincreasing the intensity of a signal component that arises from theradiation reflected by a feature being processed in the substraterelative to other signal components.
 41. A method according to claim 40comprising processing signal components of the reflected radiation thatare polarized to different polarization angles.
 42. A method accordingto claim 41 comprising determining a ratio or subtraction product of thereflected radiation signal components.
 43. A method according to claim42 wherein the reflected radiation signal components comprise signalcomponents arising from radiation polarized at polarization angles whichare substantially parallel, or substantially perpendicular, to theorientation of the feature.
 44. A method according to claim 36 wherein(e) comprises filtering the signal to selectively pass through afrequency passband relating to an intensity modulation frequency of theradiation reflected from a feature being processed on the substrate. 45.A method according to claim 44 wherein the frequency passband iscentered about the modulation frequency.
 46. A substrate processingapparatus comprising: a chamber capable of processing a substrate; aradiation source to provide a radiation; a radiation detector to detectradiation reflected from the substrate during processing and generate asignal; and a bandpass filter to filter the signal.
 47. An apparatusaccording to claim 46 wherein the bandpass filter is adapted toselectively pass through frequencies in a frequency passband whilereducing the intensity of other frequencies.
 48. An apparatus accordingto claim 46 wherein the bandpass filter increases the intensity of asignal component arising from the radiation reflected by a feature beingprocessed on the substrate relative to other signal components.
 49. Anapparatus according to claim 46 wherein the bandpass filter selectivelypasses through signal frequencies within a frequency passband that isselected in relation to an intensity modulation frequency of radiationreflected from the feature being processed on the substrate.
 50. Anapparatus according to claim 49 wherein the frequency passband iscentered about the modulation frequency.
 51. An apparatus according toclaim 46 wherein the frequency passband comprises a range of about ±10%of the modulation frequency.
 52. An apparatus according to claim 46wherein the bandpass filter comprises an electrical signal processor.53. An apparatus according to claim 52 wherein the electrical signalprocessor comprises a digital signal processor.
 54. An apparatusaccording to claim 46 comprising a radiation polarizer adapted topolarize the radiation to a plurality of polarization angles.
 55. Anapparatus according to claim 54 wherein the radiation polarizercomprises one or more polarizing filters.
 56. An apparatus according toclaim 46 comprising a radiation polarizer to polarize the radiation to apolarization angle that is related to an orientation of a feature beingprocessed on the substrate.
 57. An apparatus according to claim 56comprising a radiation polarizer adapted to polarize the radiation to apolarization angle that is substantially parallel, or substantiallyperpendicular, to the orientation of the feature.
 58. An apparatusaccording to claim 56 wherein the feature comprises a principalorientation, and wherein the radiation is polarized to a firstpolarization angle substantially parallel to the principal orientationand a second polarization angle substantially perpendicular to theprincipal orientation.
 59. An apparatus according to claim 46 comprisinga controller adapted to process the signal to increase the intensity ofa signal component arising from the radiation reflected by the featurebeing processed on the substrate relative to other signal components.60. An apparatus according to claim 59 wherein the controller processessignal components of reflected radiation that are polarized at differentpolarization angles.
 61. An apparatus according to claim 59 wherein thecontroller determines a ratio or subtraction product of the reflectedradiation signal components.
 62. An apparatus according to claim 61wherein the reflected radiation signal components comprises signalcomponents arising from radiation polarized at polarization angles whichare substantially parallel, or substantially perpendicular, to theorientation of the feature.
 63. A substrate processing methodcomprising: (a) placing a substrate in a process zone; (b) settingprocess conditions of an energized gas to process the substrate; (c)providing a source of radiation in the process zone; (d) detectingradiation that is reflected from a substrate during processing of thesubstrate and generating a signal; and (e) bandpass filtering thesignal.
 64. A method according to claim 63 wherein (e) comprisesincreasing the intensity of a signal component arising from theradiation reflected by a feature being processed on the substraterelative to other signal components.
 65. A method according to claim 63wherein (e) comprises selectively passing through frequencies in afrequency passband while reducing the intensity of other frequencies.66. A method according to claim 63 wherein the frequency passbandrelates to an intensity modulation frequency of the radiation reflectedfrom the feature being processed on the substrate.
 67. A methodaccording to claim 66 wherein the frequency passband is centered aboutthe modulation frequency.
 68. A method according to claim 63 comprisingproviding radiation polarized at one or more polarization angles thatare selected in relation to an orientation of a feature being processedon the substrate.
 69. A method according to claim 68 wherein theradiation is polarized at a plurality of polarization angles.
 70. Amethod according to claim 68 wherein the one or more polarization anglescomprise a polarization angle is substantially parallel, orsubstantially perpendicular, to the orientation of the feature.
 71. Amethod according to claim 68 wherein the one or more polarization anglescomprise a first polarization angle substantially parallel to thefeature orientation and a second polarization angle substantiallyperpendicular to the feature orientation.
 72. A method according toclaim 71 wherein the feature is a trench having a principal orientation,and wherein the one or more polarization angles comprise a polarizationangle that is related to the principal orientation of the trench.
 73. Amethod according to claim 68 comprising processing signal components ofreflected radiation that are polarized at the one or more polarizationangles.
 74. A method according to claim 73 comprising determining aratio or subtraction product of the reflected radiation signalcomponents.
 75. A method according to claim 73 wherein the reflectedradiation signal components comprises signal components arising fromradiation polarized at polarization angles which are substantiallyparallel, or substantially perpendicular, to the orientation of thefeature.
 76. A substrate processing apparatus comprising: a processchamber comprising a substrate support, gas inlet, gas energizer, gasexhaust, and a wall having a recess with a window therein and a maskover the window; and a process monitoring system capable of monitoring aprocess that may be conducted in the process chamber, through the windowin the recess of the wall.
 77. An apparatus according to claim 76wherein the mask covers the window.
 78. An apparatus according to claim76 wherein the mask comprises one or more apertures sized to reduce thedeposition of process residues therein.
 79. An apparatus according toclaim 78 wherein the apertures comprise an aspect ratio of at leastabout 0.25:1.
 80. An apparatus according to claim 78 wherein theapertures comprise an aspect ratio of less than about 12:1.
 81. Anapparatus according to claim 78 wherein the apertures comprise anopening size of from about 0.1 to about 50 mm.
 82. An apparatusaccording to claim 78 wherein the apertures comprise a depth of fromabout 0.5 to about 500 mm.
 83. An apparatus according to claim 76further comprising an electromagnetic field source adapted to maintainan electromagnetic field about the window.
 84. An apparatus according toclaim 83 wherein the electromagnetic field source comprises anelectrical or magnetic field source.
 85. An apparatus according to claim76 wherein the process monitoring system comprises a radiation detectorto detect a reflected radiation and generate a signal, and a filter tofilter the signal.
 86. An apparatus according to claim 76 furthercomprising a radiation polarizer.
 87. A method of processing a substratein a chamber, the method comprising: placing the substrate in thechamber; providing an energized gas in the chamber to process thesubstrate; masking a window provided in a recess in a wall of thechamber; and monitoring a process that may be conducted in the chamberthrough the window in the recess in the wall.
 88. A method according toclaim 87 wherein masking the window comprises reducing deposition ofprocess residues on the window.
 89. A method according to claim 87wherein masking the window comprises covering the window with a maskhaving one or more apertures.
 90. A method according to claim 87comprising maintaining an electromagnetic field about the window.
 91. Amethod according to claim 90 comprising preferentially localizing theelectromagnetic field about the window.
 92. A method according to claim87 comprising detecting a substrate reflected radiation, generating asignal, and a filtering the signal.
 93. A method according to claim 92comprising polarizing a radiation that is reflected from the substrateand detecting the radiation, and processing the signal.
 94. A methodaccording to claim 93 comprising polarizing the radiation to one or morepolarization angles related to an orientation of a feature beingprocessed on the substrate.
 95. A substrate etching method comprising:(a) placing a substrate in a process zone, the substrate having a firstlayer with an initial thickness; (b) providing energized gas in theprocess zone to etch features in the first layer in the substrate, thefeatures having a principal orientation; (c) polarizing radiation at oneor more of (i) a first polarization angle that is substantially parallelto the principal orientation of the features being etched on thesubstrate, and (ii) a second polarization angle that is substantiallyperpendicular to the principal orientation; (d) directing the polarizedradiation onto the substrate; (e) detecting an intensity of thepolarized radiation reflected from the substrate and generating a signaltrace; and (f) evaluating the signal trace to identify a feature of thesignal trace that occurs when a predetermined thickness of the firstlayer remains on the substrate to determine an endpoint of the process.96. A method according to claim 95 comprising evaluating the signaltrace relative to a stored trace or feature.
 97. A method according toclaim 95 comprising the initial steps of (1) determining a signal traceof an intensity of a reflected radiation from a substrate being etched,and (2) selecting the feature from the signal trace.
 98. A substrateetching apparatus comprising: (a) a chamber comprising a substratesupport, gas supply, gas energizer, and gas exhaust; the chamber capableof maintaining an energized gas therein to etch features in thesubstrate, the features having a principal orientation; (b) a radiationpolarizer to polarize radiation to one or more of (i) a firstpolarization angle that is substantially parallel to the principalorientation of the features being etched in the substrate, and (ii) asecond polarization angle that is substantially perpendicular to theprincipal orientation; (c) a radiation detector to detect an intensityof the polarized radiation reflected from the substrate and generate asignal trace; and (d) a controller to evaluate the signal trace toidentify a feature of the signal trace that occurs when a predeterminedthickness of the first layer remains on the substrate to determine anendpoint of the process.
 99. An apparatus according to claim 98 whereinthe controller evaluates the signal trace relative to a stored trace orfeature.